OQL query to find empty maps

Question

Hello,
I'm trying to find instances of a Map inside a heapdump using VisualVM's "OQL Console".
But I can't figure out how to access the size (or count) property of a map.
What I tried was the following:
select m from java.util.concurrent.ConcurrentHashMap m where m.count == 0But that didn't return anythong (although I know that there are empty maps in the heap by looking at the instances itself)
Then I found another example which used some kind of casting to ensure that m.count would be treated as a number:
select m from java.util.concurrent.ConcurrentHashMap m where m.count * 1 == 0That seemed to returned instances, but when I tried to find the non-empty ones using
select m from java.util.concurrent.ConcurrentHashMap m where m.count * 1 > 0I didn't return anything, and I know (again from looking at the instances) that there are non-empty maps in there.
I also tried replacing m.count with m.size in all examples, but still no go.
I'm sure I'm missing something obvious with the OQL syntax, but what?

Answer 1

Hello,
Just pass the user list you want to count and not admin users or other default users.
SELECT owner, table_name, num_rows
      FROM dba_tables
      WHERE owner IN ('MYUSER','OTHERUSER');or this
DECLARE
   CURSOR mycur
   IS
      SELECT owner, table_name, num_rows
      FROM dba_tables
      WHERE owner NOT IN ('SYS', 'SYSTEM', 'SYSMAN', 'OUTLN')
            AND iot_name IS NULL;
   v_sql     VARCHAR2 (100);
   v_count   NUMBER := 0;
BEGIN
   FOR cur IN mycur
   LOOP
      v_sql     := NULL;
      v_count   := 0;
      v_sql     :=
         'select count (*) from ' || cur.owner || '.' || cur.table_name;
      EXECUTE IMMEDIATE v_sql INTO v_count;
      IF (v_count = 0)
      THEN
         DBMS_OUTPUT.put_line(   'Table name = '
                              || cur.table_name
                              || ' rows '
                              || v_count);
      END IF;
   END LOOP;
END;Regards